In automated high-speed printing presses the pile of printed sheets loaded on a skid is changed immediately after reaching the final pile height. This process must be made without high acceleration forces and the pile should be formed in a stable and exact manner to prevent a pile slippage during pile lowering, raising and transportation and that high acceleration during pile movement should not cause pile slippage.
Air layers between the sheets established during piling are the main cause of pile instability. The air escapes after some time by itself due to the weight of the sheets. But with high production speeds of modern paper processing machines and the targeted short transportation distances the time is usually too short for venting the paper pile.
Therefore apparatus and methods are known for speeding pile venting before or during the transportation.
An apparatus is described in German patent No. 3,403,209 A1 for eliminating air inclusions by a smoothing tool shaped as a brush or roller for removal of trapped air below the smoothing tool during the pile movement transporting apparatus. A disadvantage of this apparatus is that it can be only used when the pile is moved. The possibility of a pile slippage cannot be fully eliminated until the material is compacted. Therefore this apparatus does not provide any suggestion as to measures for removing a pile from the delivery of a printing press without slippage of the pile.